The town square of San Cristobal de Las Casas has free wireless.  There are benches you can sit at to surf the web if you don't mind peddlers coming up to you to sell you things.   

There are many restaurants in San Cristobal de Las Casas that have free WI FI.

One is Tierra Adentro, located on the main east-west street, Real de Guadalupe in the first block on the north side of the street. It is one-half block from the zocalo. This is a gathering place for many people supporting co-ops and looking for a nice space to drink coffee, meet and eat.

The Madre Tierra Restaurant located on Insurgentes, three blocks north of the zocalo also has Wi FI and a lovely atmosphere.

The Kinoki tea house and cultural center on Benito Juarez, right off the Andador Guadupano, on the second floor has WIFI and shows films.

Other places include La Casa de Pan and the Mayambe, located on Calle 5 de Mayo.

Also please enjoy free WiFI at Plaza Gallery Hotel & Boutique located in the "centro" of the city. Nice view of the Cathedral Church.

A large number of the town's establishments offer this service now.